The present invention relates generally to pattern recognition systems, and, more particularly, relates to a pattern recognition system for locating the geometric center lines or center points of distinguishable areas on a generally planar surface. The invention has many areas of possible application, but is described in the specific context of a system for locating bonding pads on semiconductor circuit (IC) chips. An IC chip is an interconnected array of active and passive electrical elements formed on a single semiconductor substrate, and capable of performing at least one electronic circuit function. The necessary electrical connections between IC chips in any arrangement of microcircuitry are made by external wire connections to terminal points taking the form of relatively large metallic bonding pads formed on each chip substrate. For any chip of a particular type or design, the bonding pads are located uniformly on the chip to a fairly high degree of precision. However, it is essential to be able to determine the position and orientation of the chip, and therefore the positions of the bonding pads with respect to a bonding machine, in order to bond conducting wires to them. It is also useful to be able to determine the position and orientation of the chip for other purposes, such as assembly or testing of chips.
The attachment of bonding wire to bonding pads on IC chips has, until recently, been a manual operation, performed by an operator using a wire bonding machine which includes a high-power microscope and manual controls allowing movement of the chip with respect to a bonding tool. Semi-automatic wire bonding machines have become available, and these perform the required bonding operations in an automatic pre-programmed sequence, but still require operator intervention in order to position each chip precisely at the start of the sequence. In other words, the position and orientation of each chip is first determined by the operator, then the semi-automatic machine utilizes this positional information to perform the bonding operation.
In another assembly operation in the fabrication of microelectronic circuitry, a chip assembly machine is utilized to pick up chips sequentially from an assembly station, and to place them in predetermined positions on a substrate. This machine also operates semi-automatically, but requires the chips to be properly aligned and oriented at the input station. Again, then, there is a need for some means for automatically determining the position and orientation of the chips.
There are other operations in the fabrication and testing of microcircuitry components which could also usefully employ some means for locating the bonding pads on IC chips. By way of further example, chips of various types may have to be sorted, and they can usually be reliably identified by their particular patterns of bonding pads. Another application is in the area of chip testing, wherein test probes must be placed in contact with various bonding pads. Again, if the bonding pads could be accurately and readily located without operator intervention, testing procedures could be substantially accelerated.
Accordingly, it will be appreciated that the fabrication of microcircuitry has a number of related needs requiring the detection and location of distinguishable areas on an essentially two-dimensional surface. The present invention satisfies these needs, and can also be usefully employed in many other applications involving the accurate location of distinguishable areas in a field of interest. For example, in any automated manufacturing process in which parts are to be coupled together, manual intervention is often required to orient and position the parts. Use of the present invention in such cases can result in complete automation of the assembly process.